The present invention comprises a new and distinct variety of Metasequoia glyptostroboides (`Dawn Redwood`).
The `Dawn Redwood` is an excellent tree for landscaping in parks, golf fields, streets or river side. The leaves are deciduous, opposite in arrangement, and linear, flattened, straight or slightly curved, pectinately arranged, 1.25 cm long and 0.16 cm broad on mature trees. Its leaf color is bright green above changing to brown in fall and can be an excellent orange-brown to red brown. The habit is pyramidal, conical with a single straight trunk in youth, but, supposedly develop a broad-rounded crown with age. Furthermore, growth rate is fast (15 m in 15 to 20 years).
Conventionally, there are two varieties as follows.
(1) `National`--Habit conspicously narrow -- pyramidal, which was selected in 1958 at the National Arboretum. It showed 18 m high, 8.4 m wide at 23 years old.
(2) `Sheridan Spire`--More upright than typical for the species.
Namely, two varieties are characterized by habit, especially branching pattern. However, as the leaf color is the same as compared with the common `Dawn Redwood`, they do not give a strong impact to us from a visual point of view.
The new variety of `Dawn Redwood` is characterized by the leaf color and slightly slower growth rate. The new variety also roots readily through cutting with and without hormones or other root stimulating materials. The leaves are distinctly bright yellow as if its color is golden, especially observed under strong sunlight. Furthermore, the growth rate is slightly slower than the normal type, since the photosynthetic ability is lower as compared to the common `Dawn Redwood` having green leaves.
The new variety has been found to retain its distinctive characteristics through successive propagations.
The new variety is a mutant introduced by x-ray irradiation. In April, 1974, approximately 200 g of Metasequoia glyptostroboides dry seeds were irradiated for one hour by 1000 R of x-ray. These treated seeds were sown into sowing boxes and raised by the routine method. Among 35,800 of treated seeds, approximately 28,000 of seed germinated and grew normally. But, 7,800 of the seeds could not germinate, perhaps due to damage from the X-ray treatment. Among the 28,000 seedlings, approximately 20,000 seedlings were healthy. From the 20,000 healthy seedlings, I discovered only one distinct seedling having bright yellow leaves. After selecting, this new and distinct individual has been propagated by repetitive cuttings. However, the characteristic has never changed, and always retained its distinctive characteristics.
In 1977, a parent stock (mutant) was planted at Kameyama Breeding Station, Institute for Forest Tree Improvement, New Oji Paper Co., Ltd. in Mie, Japan. In 1992, six individuals of this variety were planted at an arboretum in Kameyama Breeding Station to compare the characteristics with the common `Dawn Redwoods` (common type).